This invention relates to formation of metal dies or molds, and in particular to a method for forming a contoured mold surface by progressively etching the surface of a workpiece until the mold configuration is formed in the workpiece.
Metal molds or dies can be formed in several different manners. The present invention relates to manufacture of molds or dies by etching techniques where an etchant, such as an acidic bath, is used to etch a metal surface progressively in order to form the mold or die. Throughout the remainder of this description, the terms "mold" and "die" will be used interchangeably to mean a tool formed from a workpiece and which has a contoured surface for use in the production in quantity of three-dimensional products of metal, plastic or the like.
U.S. Pat. No. 4,325,779, issued on an invention of the same inventor as this application, relates to a method for forming a mold surface by etching techniques. However, in the disclosed method of U.S. Pat. No. 4,325,779, the technique is laborious, requiring removal of portions of a coating covering the mold workpiece surface, application of an etchant to etch any thus exposed metal, removal of the etchant and cleaning of the mold, reapplication of the coating to the entire mold workpiece surface, and then repetition of the procedure until sufficient depth of etching has been effected to form the mold. The method is labor intensive and quite slow due to the necessity for continual cycles of manual application and removal of the coating material and the etchant.
U.S. Pat. No. 3,290,192 discloses a method of continually forming surfaces by etching techniques. An item to be etched is immersed in an etching bath and a heated die is brought into contact with the surface of the item repeatedly in order to etch the surface. The etchant is kept relatively cool to minimize its etching capabilities, while the repeated pulsation of the die is intended to continually replenish fresh etchant between the tool face and the surface being etched. There is no coating to protect the surface being etched, requiring careful control of the temperature of the etchant and of the nature of the etchant to assure that other areas of the surface are not inadvertantly etched where etching is not desired.